Solid-state imaging device with shutter operation in sync with signal charge reset and method of driving same

[0002] 1. Field of the Invention

[0003] The present invention relates to a solid-state imaging device such as a CCD linear sensor, a CCD area sensor or the like and a method for driving such a solid-state imaging device.

[0004] 2. Description of the Related Art

[0005] It has been proposed that in a color CCD linear sensor having a plurality of sensor lines be provided with a shutter function by which the amplitudes of a plurality of signals from the sensor lines can be controlled.

[0006] A main purpose of such a shutter function is, for example, it use in a color linear sensor having three sensor lines of R(red), G(green) and B(blue), to adjust the white balance of the output voltages from the R, G and B sensors. If the same accumulating time is set, the magnitudes of each of the R, G and B output voltages are different depending on their sensitivities. This leads to the difference of dynamic range in the R, G and B output voltages.

[0007] In order to cope with this problem, a correction is performed such that in the latter stage of the signal processes. the output levels are arranged by varying each of the gains of R, G, B and, particularly if a higher quality of an image is required, the output levels of RGB are required to be arranged before the adjustment of gain, namely, just at the CCD output.

[0008] Accordingly such a method is used in which if it is assumed that τ_ROGis a period from a time when a reading gate pulse is applied to a time when the next reading gate pulse is applied, the τ_ROGis set to a charge accumulating period to the sensor portion (this is defined as 1H period), and then an effective accumulating period each of the R,G,B is varied by a shutter pulse input.

[0009] A 1H period consists of a period for transferring a signal charge, namely, an effective signal period and the subsequent non-transfer period.

[0010] In a prior art, when this effective accumulating period is to be set, the input of the shutter pulse (for example, of making the shutter pulse off) is set in the period other than the effective signal period, namely, the non-effective period. That is, if the effective signal period is set as the input period of the shutter pulse, for example, a potential of a common semi-conductor well area on a semi-conductor substrate side fluctuates as a result of the input of shutter pulse and therefore the wave form of an output signal also fluctuates owing to the influence of the coupling of shutter pulse to affect on the quality of an image. Accordingly, the input time of the shutter pulse is set in a so-called non-transfer period other than the effective signal period.

[0011] However, if the input time of the shutter pulse is set in the non-transfer period other than the effective signal period, a variable range of the signal charge accumulating time is so limited that there is no marginal time, because the remaining period the shutter operation becomes is a signal charge accumulating time. Accordingly, if the effective accumulating time is to be set longer, the τ_ROGis set as a longer time and the non-transfer period must be made long. At this time, such a drawback is produced that the signal processing time on a set increases.

[0012] In view of such aspect, it is an object of the present invention to propose a solid-state imaging device and a method of driving such a solid-state imaging device which enables the shutter operation at anytime in and out of the effective signal period.

[0013] According to a first aspect of the present invention, a solid-state imaging device includes a sensor portion for accumulating a signal charge produced by photoelectric conversion, a charge transfer register for transferring the signal charge, a charge/voltage converting portion connected to the charge transfer register, and a means for carrying out a shutter operation for discharging the charge accumulated by the sensor unit in synchronization with a signal charge reset period of the charge/voltage converting portion.

[0014] According to a second aspect of the present invention, a method is one of driving a solid-state imaging device having a sensor portion for accumulating a signal charge generated by photoelectric conversion, a charge transfer register, and a charge/voltage converting portion connected to the charge transfer register. The method includes a step of carrying out a shutter operation for discharging a charge accumulated by the sensor portion in synchronization with a reset period of the charge/voltage converting portion.

[0015] According to a third aspect of the present invention, a method is one of driving a solid-state imaging device having a plurality of sensor portions and a plurality of sensor lines for accumulating charges generated by photoelectric conversion and a plurality of charge transfer registers for transferring the signal charges and a charge/voltage converting portion connected to the plurality of charge transfer registers. The method includes a step of carrying out a shutter operation for discharging the charges accumulated by the sensor lines in synchronization with a reset period of the charge/voltage converting portion.

[0016] FIG. 1 is a diagram showing a color CCD linear sensor according to the present invention;

[0017] FIG. 2 is a timing chart of input pulses to the color CCD linear sensor according to the present invention;

[0018] FIG. 3 is a timing chart showing examples of a reset pulse φ_RS, a shutter pulse φ_SHUTand an output wave form V_OUTaccording to the present invention; and

[0019] FIG. 4 is a timing chart showing other examples of the reset pulse φ_RS, the shutter pulse φ_SHUTand the output wave form V_OUTaccording to the present invention.

[0020] A solid-state imaging device according to the present invention comprises a sensor portion, a charge transfer register, and means for performing a shutter operation in synchronism with a reset period of a charge voltage converter portion.

[0021] The solid-state imaging device according to the present invention is a linear sensor having a plurality of sensor lines and being capable of controlling the amplitude of output signals from the sensor lines by a shutter function, and a means for performing a shutter operation in each sensor line in synchronism with the reset period of the charge voltage converter portion.

[0022] A method of driving a solid state image sensor according to the present invention enables to perform a shutter operation in synchronism with the reset period of the charge voltage converter portion.

[0023] An embodiment of the present invention will be described below in reference with the drawings.

[0024] FIG. 1 shows an embodiment of the present invention which is incorporated in a color CCD linear sensor. In FIG. 1, a color CCD linear sensor is generally designated by reference numeral 1. The color CCD linear sensor 1 is formed of a plurality of sensor lines, in this embodiment three sensor lines, which are comprised of a single linear sensor (an image element), namely, a R(red) linear sensor 2R, a G(green) linear sensor 2G and a B(blue) linear sensor 2B.

[0025] The R linear sensor 2R, the G linear sensor 2G and the B linear sensor 2B have a R sensor array 3r, a G sensor array 3gand a B sensor array 3brespectively, each array including a plurality of sensor portions 3. On one sides of the sensor arrays 3r, 3gand 3bthere are provided charge transfer registers (which are referred to as CCD registers) 4r, 4gand 4b, which are for example constructed as two-phase drive CCDs, via reading gate portions 5r, 5gand 5brespectively while on the other sides of the sensor arrays 3r, 3gand 3bthere are provided shutter drain regions 7r, 7gand 7bvia shutter gate portions 6r, 6gand 6brespectively.

[0026] Adjacent to the end stage of each of the CCD registers 4r, 4g, 4b, an output gate portion 11 and a floating diffusion region 12 which becomes a charge voltage converter unit are formed and further, a reset gate portion 13 and a reset drain 14 adjoining the floating diffusion region are formed. An output circuit 15 is connected to the floating diffusion region 12.

[0027] A reading gate pulses φ_ROGis applied to the reading gate portions 5r, 5gand 5b, a reset pulse φ_ROGis applied to the reset gate portion 13 and a fixed voltage is applied to the output gate portion 11.

[0028] Two-phase drive clock pulses φ₁and φ₂are applied to the CCD registers 4r, 4gand 4band particularly a drive clock pulse φ_LHwhich is the same to the φ₁is applied to the end stage of the transfer portion.

[0029] On the other hand, a shutter means is formed of each of the shutter gate portions 6r, 6gand 6band the shutter drain regions 7r, 7gand 7b. When shutter pulses φ_SHUT-R, φ_SHUT-Gand φ_SHUT-B(See FIG. 2) are applied to the shutter gate portions 6r, 6gand 6brespectively, the signal charges which have been accumulated in the sensor arrays 3r, 3gand 3bare discharged to the shutter drain regions 7r, 7gand 7bvia the shutter gate portions 6r, 6gand 6brespectively.

[0030] As shown in FIG. 2, in this color CCD linear sensor 1, the period from the time when the reading gate pulse φ_ROGis applied to the time when the subsequent reading gate pulse φ_ROGis applied is τ_ROGand this τ_ROGis set as a period for accumulating the charge in the sensor portion 3 (which is defined as 1H period). This 1H period consists of an effective signal period T_Afor transferring and outputting the signal charge and the subsequent non-transfer period T_B.

[0031] In the color CCD linear sensor 1, the signal charges which have been accumulated in the respective sensor arrays 3r, 3gand 3bby means of photo-electric conversion are read simultaneously to the CCD registers 4r, 4gand 4brespectively by applying the reading gate pulse φ_ROGto the reading gate portions 5r, 5gand 5b. If the two-phase drive clock pulses φ₁, φ₂and φ_LHare applied to the CCD registers 4r, 4gand 4b, the charges are transferred during the effective signal period T_Aof FIG. 2 and the signal charge at each one pixel (sensor portion) is read via the floating diffusion regions 12 as an output signal by the output circuit 15. The floating diffusion region 12 is reset when the reset pulse φ_RSis supplied to the reset gate portions 13 at each pixel.

[0032] The non-transfer period T_Bfrom the end of the effective signal period T_Aand before the subsequent reading gate pulse φ_ROGis applied is a state such that no charge is transferred.

[0033] Thus, according to the present embodiment, at any time during the 1H period, namely, whether during the effective signal period T_Aor the non-transfer period T_B, the input of the shutter pulses φ_SHUT-R, φ_SHUT-G, and φ_SHUT-Bcan be performed. At this time, the shutter pulses φ_SHUT-R, φ_SHUT-Gand φ_SHUT-Bare input in synchronism with the reset period To of the floating diffusion region 12 or the charge voltage converter portions. In this way, the shutter operation can be performed during the reset period T_RSof the reset pulse φ_RS.

[0034] For example, in the embodiment of FIG. 3, during the period T_RSwhen the reset pulse φ_RSis applied in the effective signal period T_A, the shutter pulse φ_SHUTis off.

[0035] In the embodiment of FIG. 4, the shutter pulse φ_SHUTis applied during the period T_RSwhen the reset pulse φ_RSis applied in the effective signal period T_A.

[0036] In the embodiment shown in FIG. 2, the shutter pulse φ_SHUT-Ris not input to the R linear sensor 2R which has the lowest sensibility among the R linear sensor 2R, the G linear sensor 2G and the B linear sensor 2B, but the shutter pulses φ_SHUT-Gand φ_SHUT-Bare input to the G linear sensor 2G and the B linear sensor 2B respectively. In this case, the effective accumulating times of the R linear sensor 2R, the G linear sensor 2G and the B-linear sensor 2B become t_R, t_Gand t_Brespectively.

[0037] In this way, if the shutter pulses φ_SHUT(φ_SHUT-G, φ_SHUT-B) are input in synchronism with the reset period T_RS, the influence of the coupling is produced only in a reset phase Re in an output wave form V_OUTof FIG. 3 and FIG. 4 but no influence of the coupling is produced in a precharge phase P and a data phase D which are required in a correlation double sampling circuit (CDS) for removing a noise.

[0038] Accordingly, the input times of the shutter pulses φ_SHUT(φ_SHUT-R, φ_SHUT-Gand φ_SHUT-B) can be set at any time in the 1H period whether in or out the effective signal period T_Aand therefore the variable ranges of the effective accumulating times t_R, t_Gand t_Bof respective colors by the shutter control can be set wider than that of the prior art. Further, the influence of the coupling of the shutter pulses φ_SHUTon the wave form of output signal can be suppressed.

[0039] In the above embodiment, the floating diffusion region is used as the charge voltage converter portion, but the floating gate or the like can be also used.

[0040] In the above embodiment, the present invention is applied to the color CCD linear sensor 1 having three single linear sensors 2R, 2G and 2B but may be applied to a color CCD linear sensor having a plurality of, other than three, single linear sensors. Further, the present invention can be applied to a single color linear sensor.

[0041] The present invention can also be applied to a CCD area sensor. In this case, the shutter operation is performed in synchronism with the reset period of the charge voltage converter portion which is connected to a horizontal transfer register.

[0042] According to the present invention, the influence of the coupling based on the shutter operation is not affected on the wave form of output signal and the shutter operation can be performed at anytime of the period including the period of reading a signal. Accordingly, the variable range of the effective accumulating period by the shutter control can be set wider than that of the related art.

[0043] Having described preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the present invention is not limited to the above-mentioned embodiments and that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit or scope of the present invention as defined in the appended claims.